add activemerchant gem
added ActiveMerchant credit card processing
Updates student upgraded status after purchase
Merge branch 'feature-order' into dm-working
Added methods to prevent/enable non-free Lessons from being displayed if current Student is not upgraded.
Merge branch 'feature-paid-lessons' into feature-order
Merge branch 'feature-order' into dm-working
updated show view
Merge branch 'master' into dm-working
fixed upgraded check branching
Merge branch 'dm-working'